Classroom questions represent a potentially powerful tool for interacting with students and stimulating critical thinking. However, the efficacy of the question-and-answer approach to teaching is influenced by many factors, such as the type and cognitive level of questions asked as well as students' response time. To examine these factors and identify optimal strategies for asking questions in college classrooms, the authors assessed the use of questions in lecture-style science classes at a large public research university in the Southeastern United States. Results revealed several guidelines that could help instructors refine their questioning strategies to enhance student learning. (Contains 3 figures and 1 table.)